The present invention relates to an automatic clutch control apparatus for use between an engine and a transmission on a motor vehicle for transmitting and interrupting the torque produced by the engine.
There has been put to use an electronically controlled automatic vehicular transmission system including a gear transmission with parallel shafts, an automatic friction clutch, and an electronic control unit comprising a microcomputer for controlling the transmission of engine torque.
The amount of engagement of the automatic clutch and the speed of operation thereof in such an electronically controlled automatic transmission system are determined based on the amount of depression of an accelerator pedal, the rotational speed of the engine, and the rotational speed of the input shaft of the transmission.
The effective stroke (i.e., effective operation range) of a clutch from a position to start engaging the clutch (i.e., a position to start partly engaging the clutch) to a position to fully engage the clutch, varies due to manufacturing variations and the wear of the clutch driven plate.
For controlling the amount of engagement of the clutch when starting the vehicle or in other instances, it is desirable that the clutch stroke positions serving as a control reference be determined with respect to each motor vehicle.
In view of such a demand, the applicant has proposed, as disclosed in Japanese Laid-Open Patent Publication No. 60-11722 (corresponding to U.S. Pat. No. 4,629,045), a clutch control apparatus for determining the position to fully engage a clutch and the position to start engaging the clutch (i.e., the position to start partly engaging the clutch) by learning them, and controlling the clutch based on the learned positions.
Manufacturing variations and wear on the driven plate of a clutch can be compensated for by controlling the clutch based on the learned positions to fully engage the clutch and to start engaging the clutch.
The inventor has found the following facts as a result of research and experimentation.
FIG. 3 shows the relationship between a clutch stroke and a transmitted torque.
FIG. 3 illustrates different clutch characteristic curves (1), (2), and (3) of three clutches. The clutch having the characteristic curve (1) has a learned position A to start engaging the clutch, the clutch having the characteristic curve (2) has a learned position B to start engaging the clutch, and the clutch having the characteristic curve (3) has a learned position C to start engaging the clutch.
It has experimentally been found that these clutches (1), (2), and (3) having the different learned positions to start engaging the clutches have the same clutch stroke when starting the motor vehicles incorporating the clutches.
According to the clutch control disclosed in U.S. Pat. No. 4,629,045, assuming that the clutch indicated by the curve (1) in FIG. 3 has designed clutch characteristics, the clutch indicated by the curve (2) is controlled as if it had a clutch characteristic curve (2)' passing through the point B parallel to the curve (1), and the clutch indicated by the curve (3) is controlled as if it had a clutch characteristic curve (3)' passing through the point C parallel to the curve (1).
Therefore, when the amount of engagement of the clutch indicated by the curve (2) is controlled according to the curve (2)', using the learned position (B) as a reference, a shortage of transmitted torque occurs and excessive clutch slippage is caused when starting the motor vehicle since the actual curve of that clutch is (2). When the amount of engagement of the clutch (3) is controlled according to the curve (3)', the amount of engagement becomes excessive when starting the motor vehicle, and a shock is produced because of excessive torque transmission.